Police detention clock -- arrest, s136, common law

I’m wondering if the patient is always told that the means of detention has changed from Sc 136 to common law AND how time spend on a trumped up charge thats subsequently dropped NFA affects the Sc136 time limit?
I’m trying to work out the timings arrest 10am on the 9th Sc2 started on 11th.
Luckily i can laugh at the fact the police couldn’t tell the difference between an undocumented rough sleeper who’s bladder was about to explode and a suicide bomber. I got housed in hospital for 4 months under someone else’s details. I’m now having a pig of a job proving my real identity!
The length of detention was due to the records they used my reaction to medication administered and my annoyance at not being allowed to speak to police about the sexual assualt I endured a week before the arrest